Decoupled Closely Spaced Heptaband Antenna Array for WWAN/LTE Smartphone Applications

A planar antenna array, which is closely placed with an infinitesimal distance of only 4 mm between array elements yet well decoupled by a deliberately designed small-size protruded ground, is presented. The well-designed protruded ground has two types of behaviors: reducing the coupling in between the array elements and improving impedance matching to enhance the bandwidth. At the lower bands of GSM850/900 and the upper bands of GSM1800/1900/UMTS/LTE2300/2500, the good radiation efficiencies of better than 43% and 50% respectively are obtained, and simultaneously the isolations of better than 10 dB are achieved in between the antenna elements. A prototype is made and tested, with S-parameters, radiation efficiency, radiation pattern, and envelope correlation coefficient (ECC) presented.